Four U.S. swimmers, including gold medalist Ryan Lochte, were robbed in Rio de Janeiro. / AP-Yonhap

By Choi Ha-young

Armed thieves robbed four American swimmers in Rio de Janeiro on Sunday, again raising concerns about safety during the international event.

"They pulled out their guns, they told the other swimmers to get down on the ground — they got down on the ground," Ryan Lochte, gold medalist in the men's 4x200-meter freestyle relay told USA Today.

The swimmers, who were not harmed, were returning to their accommodation by taxi after hanging out with French Olympians in the Rodrigo de Freitas area in the southern part of Rio.

"Their taxi was stopped by individuals posing as armed police officers. They demanded the athletes' money and other personal belonging," U.S. Olympic Committee spokesperson Patrick Sandusky said in a statement.

The Brazilian city's unstable security has been a chronic problem.

On Aug.10, Belgian judoka Dirk Van Tichelt was also assaulted by a thief, suffering a black eye.

A bus carrying international journalists was hit by two stones on the same day, causing minor injuries to 12 people.